The present invention is directed generally to brewing apparatus for heated beverages, such as coffee and tea, and more particularly to brewing apparatus wherein a supply of hot water for producing the beverage is maintained at a predetermined constant brewing temperature within a heated reservoir by circuitry continuously responsive to the temperature of the contents.
One known type of brewing apparatus for making heated beverages includes a reservoir within which a volume of water to be displaced is heated by a resistance heating element to a predetermined brewing temperature. In a preferred form of such brewing apparatus, such as the coffee maker described in U.S. Pat. No. 4,413,552 to Donald L. Daugherty, heated water is displaced from the top portion, or outlet zone, of the reservoir by cool or cold water entering the bottom portion, or inlet zone, and discharged onto ground coffee or tea held in a brewer funnel lined with a disposable filter. The freshly brewed coffee or tea discharging from the brewer funnel is collected in a serving beaker.
Cold water is admitted in batches of predetermined volumes to the reservoir of such brewing apparatus to displace the heated water delivered to the brewing funnel. In pour-in type beverage brewers, such as described in the afore-identified U.S. Pat. No. 4,413,552, a quantity of cold water sufficient to produce the desired volume of beverage to be brewed is poured into a cold water basin from which it flows by gravity into a hot water tank to displace an equal quantity of hot water to the brewing funnel. In automatic type beverage brewers, such as described in U.S. Pat. No. 3,793,934, a valve is opened by electrical or manual means to periodically deliver the batches of cool or cold water to the apparatus.
Prior art beverage brewers, such as described in U.S. Pat. No. 3,736,155, have employed a bimetallic switch which energized the resistance heating element when the water temperature in the reservoir fell to a predetermined minimum below the brewing temperature, and de-energized the heating element when the water temperature in the reservoir rose to a predetermined maximum above the brewing temperature. The difference between such minimum and maximum temperatures was typically from 6 to 8 degrees Fahrenheit. In this way, water in the hot water tank was cycled between minimum and maximum temperatures, through an average temperature corresponding to the desired brewing temperature. Thermostat switches responsive to temperatures sensed by bulb and capillary type temperature sensing elements disposed in the hot water tanks have also been used. To minimize the frequency of such cycling between minimum and maximum hot water temperatures, an auxiliary heat source in the form of a continuously-excited resistance heating blanket was wrapped around the reservoir to provide a continuous source of heat for the water contained within the reservoir.
For maximum operating efficiency and minimum scale formation within the reservoir, it is desirable that the spread between minimum and maximum hot water temperatures be minimized and preferably substantially eliminated. The present invention is directed to an improved beverage maker of the type maintaining a supply of hot water wherein the heating element in the hot water reservoir is periodically excited over a variable duty cycle to maintain a substantially constant water temperature in the reservoir, thereby minimizing scaling, maximizing operating efficiency and eliminating the need for a heated jacket.
Accordingly, it is a general object of the present invention to provide a new and improved beverage brewer.
It is a more specific object of the present invention to provide a new and improved beverage brewer having improved operating efficiency and reduced tendency for scale formation.
It is a further object of the present invention to provide a new and improved beverage brewer of the type having an internal reservoir for maintaining a supply of heated water wherein the temperature of the water is maintained at a substantially constant predetermined brewing temperature.
Still another object of the invention is the provision of a new and improved beverage brewer of the type housing a hot water tank from which hot water is displaced to a brewing funnel and wherein the water temperature is maintained substantially constant so as to eliminate the need to provide the tank with a heated jacket and thereby avoiding the detrimental effects of such blankets, manifested in corrosion and cracking of the tank wall.
It is a still further object of the present invention to provide a new and improved beverage brewer of the type having an internal hot water reservoir wherein a heating element in the reservoir is periodically excited over a variable duty cycle to maintain a substantially constant predetermined brewing temperature.